1. Field of the Invention
This invention relates, in general, to engine diagnostic devices and, more specifically, to engine diagnostic devices which detect malfunctions, such as deficient combustion, in the cylinders of an internal combustion engine.
2. Description of the Prior Art
A variety of engine diagnostic systems have been developed to diagnose the operating condition of an internal combustion engine. Such diagnostic systems have typically employed sensors mounted on an engine for detecting a pre-determined amount of angular rotation of a rotatable element of an engine, such as rotation of the crankshaft. Such angular positions are generally detected by sensing the passage of gear teeth of the flywheel ring gear past a sensor. The time interval between successive flywheel gear teeth is determined and then processed to provide a manifestation of an engine operating condition.
Systems utilizing such a measurement technique are disclosed in U.S. Pat. Nos. 4,015,467; 4,016,753 and 4,055,993. In the two former listed patents, speed measurements made while the engine is accelerating are processed to yield a starting speed, stopping speed and elapsed time measurements which can be utilized to provide torque and horsepower measurements for the engine. In the later patent, the measured time intervals during acceleration of the engine are processed to provide speed measurements of the engine itself.
In U.S. Pat. No. 4,055,993, speed measurements of an engine are determined by clocking the rotation of teeth on the flywheel of the engine. The time measurements for a pre-determined angular rotation to the flywheel are analyzed to provide speed measurements for the engine. In U.S. Pat. No. 4,348,893, an engine analysis detector is provided for determining the compression of an engine. The engine is compressed by means of cranking the engine without ignition. Changes in speed during the compression stroke of each cylinder are mathematically processed to yield values corresponding to the compression of each cylinder.
In U.S. Pat. No. 4,064,747, subcyclic speed measurements of an engine are made by detecting the difference between clock counts relative to each other to determine certain dynamic operating perameters of the engine. This detector may be used to determine relative power contribution of individual cylinders of the engine.
In U.S. Pat. No. 4,055,995, an engine diagnostic unit is disclosed which utilizes an acceleration burst between low and high engine speeds to provide horsepower measurements. Such measurements are compared with subsequent measurements to yield an indication of the amount of air in the fuel intake of the engine.
U.S. Pat. No. 3,972,230 discloses an apparatus and method of detecting uneven operation of individual cylinders in an engine. The engine is operated at any convenient idle speed and power cucle time periods between successive ignition times are measured. The decleration rates between successive time periods are then computed along with the average deceleration rates for respective cylinders. Individual deceleration rates exceeding the average deceleration rate for a cylinder are detected to provide an indication of uneven cylinder operation.
The data acquisition unit disclosed in U.S. Pat. No. 4,179,922 measures successive crankshaft positions during engine rotation to provide a time duration between successive crankshaft positions. Time interval samples are generated and utilized to determine the existence of any cylinder malfunction.
U.S. Pat. No. 4,295,363 discloses an apparatus for diagnosting faults in the individual cylinders of an engine. Measurements corresponding to the time intervals between successive crankshaft positions are detected in at least one engine cycle. A comparison of a standard engine cycle with a subsequent engine cycle is made and a ratio of the standard with subsequent values as compared with a threshold to provide an output indicating the existence of a faulty condition such as low compression or low power of a particular cylinder.
In all of the previously disclosed engine diagnostic systems, the time interval measurements are taken during a pre-determined engine operating mode, such as acceleration, deceleration, idling, etc. Thus, diagnosis of the operating condition of the engine takes place in only a small portion of the total engine operating range and then only for a short period of time. As such, the previously disclosed methods for detecting engine malfunctions have not been totally accurate overall engine operating conditions.
Furthermore, such previously devised engine diagnosing systems have been relatively complex in configuration thereby resulting in a large sized diagnostic device which prevents its on-board use in a vehicle, such as an automobile, truck, etc. In addition, such previously devised engine diagnostic systems have been specifically devised for use with internal combustion engine in automobiles and trucks. Such diagnostic systems have not been employed, due to their limitations, in large size diesel and marine engines as well as internal combustion engines employed on aircraft and trains.
Thus, it would be desirable to provide an engine diagnostic system which overcomes the problems associated with previously devised diagnostic systems. It would also be desirable to provide engine diagnostic systems which is able to continuously monitor engine operation over a variety of engine operating conditions, such as idling, cruising, acceleration and deceleration. It would also be desirable to provide an engine diagnostic system which is simple in configuration and small in size so as to permit it to be installed directly in a vehicle for continuous monitoring of engine performance.